1. Field of the Invention
The present invention relates to a method of sorting out defect-free workpieces blanked out of a metal sheet, and more particularly to a method of sorting out defect-free elements of a belt for use in a continuously variable transmission for automobiles.
2. Description of the Related Art
Continuously variable transmissions for use on automobiles employ an endless belt comprising a plurality of elements, each blanked out of a metal sheet, stacked in their transverse direction into an annular form and put together by endless rings.
As shown in FIG. 1 of the accompanying drawings, each of such elements, denoted by 1, comprises a body 2 and a head 5 joined to the body 2 with recesses 3, 4 defined therebetween. The body 2 has a pair of slanted edges 6, 7 on its lateral opposite sides which jointly provide a V-shaped surface for contacting a pulley of a continuously variable transmission. After the element 1 is blanked out of a metal sheet, the edges of the recesses 3, 4 and the slanted edges 6, 7 are ground by abrasive particles, and delivered by a belt conveyor or the like to a subsequent process where the element 1 is thermally treated. After a given number of elements 1 are thermally treated, they are stacked in their transverse direction into an annular form. Endless rings 13, each comprising a plurality of stacked sheet-like metal rings 12, are inserted in the respective recesses 3, 4 to bundle the elements 1 into a belt 14 for use in a continuously variable transmission.
When the element 1 is caught in a gap in the belt conveyor or thermally treated, the body 2 and the head 5 may possibly be strained or twisted. If the element 1 is strained or twisted, then when a plurality of elements 1 are stacked, the stacked elements 1 may become longer than a desired length or it may be difficult to insert the endless rings 13 into the recesses 3, 4.
When the element 1 is ground by abrasive particles or caught in a gap in the belt conveyor, the element 1 may possibly be damaged or partly broken off.
For inspecting elements 1, it has heretofore been customary for the worker to visually observe the elements 1 at the time the elements 1 are stacked. However, it is tedious and time-consuming to visually inspect all the elements 1 to be stacked. In addition, different inspection personnel have different standards for sorting out defect-free elements 1, and the manual inspection process may possibly overlook damaged or broken regions of elements 1.